Are you trying to use the standalone player or the plugin version?
When the browser launches, can you right click and see if "Debugger" appears in the menu?
If FB is launching a SWF in non-debug standalone player, then you may be running into http://forums.adobe.com/thread/624748?tstart=30
hmm, it suddenly started working again, so i guess it allright again.
I ran the uninstaller and so installed the plugin content debugger. Placed the projector content debugger app inside the player folder at Flash Builder root (could be placed anywhere I guess), and gave the path for the app to FB in preferences > Flash Builder > Profiler > Standalone.
Don't know which part who made it work, and I done the same before, but anyway it works for me now.